Optics: measuring and testing – By alignment in lateral direction
Reexamination Certificate
1999-08-11
2004-06-01
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
Reexamination Certificate
active
06744511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to exposure devices used in lithographic processes for the manufacture of liquid crystal displays, integrated circuits, thin film magnetic heads, etc., and to stage and corresponding position detection devices suitable for use with such exposure devices.
2. Description of the Related Art
Lithographic processes utilized during the manufacture of liquid crystal displays, integrated circuits, and other similar devices usually involve exposure devices. Such exposure devices have been used to image a mask pattern onto a substrate. Such exposure devices include step and repeat type devices (often referred to as a “liquid crystal stepper”) and batch transfer scanning type devices which transfer a pattern of a mask onto a plate (e.g., a glass substrate). Such devices typically scan a mask stage and a plate stage in the same relative direction with respect to a projection optical system.
Recent developments have been made in regard to exposure devices as a result of increased demand for larger liquid crystal displays, etc. Accompanying such increases, plate sizes within exposure devices have correspondingly increased. Accordingly, scan type exposure devices have been developed which are capable, of exposing a large surface compared to a stepper, and which perform exposures of plural shots with respect to one plate.
Exemplary exposure devices are illustrated in several drawing figures which have been attached to this patent document. Reference is now made to drawing figures identified as
FIGS. 5
,
6
,
7
, and
9
, respectively.
FIG. 5
shows a batch transfer type scanning exposure device.
FIG. 6
shows in more detail the stage control device
101
shown in FIG.
5
. In
FIG. 5
, a mask stage MST and plate stage PST are respectively supported on air pads (not shown in the drawing) on an upper surface plate
102
a
and a lower surface plate
102
b
which make up the body column
102
which supports the projection optical system PL. The mask stage MSK and plate stage PST are moved by linear motors
104
and,
106
in right and left scanning directions. The stator
104
a
of the linear motor
104
which drives the mask stage MST is fixed to the upper surface plate
102
a
, and its moving element
104
b
is fixed to the mask stage MST. Moreover, the position of the mask stage MST in the scanning direction is constantly measured by means of a laser interferometer
108
which is fixed to the body column
102
.
The stator
106
a
of the linear motor
106
which drives the plate stage PST is fixed to the lower surface plate
102
b
, and its moving element
106
b
is fixed to the plate stage PST. The plate stage PST is equipped with a moving table
110
to which moving element
106
b
is fixed, and with a substrate table
116
which is loaded on this moving table
110
via a Z·&thgr; movement mechanism
114
. The position of the substrate table
116
in the scan direction is constantly measured by means of a laser interferometer
112
which is fixed to the body column
102
.
The arrangement of stage control device
101
is now described with reference to FIG.
6
. As shown in
FIG. 6
, a position control loop of the plate stage PST includes interferometer
112
, a subtractor
118
, a plate stage servo operating unit
120
, a plate stage drive amplifier
122
, and linear motor
106
which is driven by the drive signal S
2
output from plate stage drive amplifier
122
. Moreover, plate stage position information S
1
from the interferometer
112
is fed back as input to the plate stage servo operating unit
120
via a differencing unit
124
. Accordingly, a speed control loop is constituted as the inner loop (minor loop) of the position control loop. The reference position is input from the reference value output unit
126
with respect to the subtractor
118
of the aforementioned position control loop. By means of the position and speed control loop of the plate stage PST constituted in this way, position and speed control of the plate stage are performed such that the position deviation, which is the difference of the reference position and the output of the interferometer
112
, becomes zero.
Similarly, a position control loop of the mask stage MST includes interferometer
108
, a subtractor
128
, a mask stage servo operating unit
130
, a mask stage drive amplifier
132
, and the linear motor
104
which is driven by the drive signal S
4
output from mask stage drive amplifier
132
. The plate stage position information S
1
, which is the output of the interferometer
112
with respect to the subtractor
128
of this position control loop, is input as the reference position. Accordingly, by means of the position control loop of the mask stage MST, slave control of the mask stage MST is performed with respect to the plate stage PST, such that the positional deviation, which is the difference of the output S
1
of the interferometer
112
and the output S
3
of the interferometer
108
, becomes zero.
Referring now to
FIG. 9
, depicted therein is another scanning type exposure device. In particular, an illuminating optical system
201
and a projection optical system
204
are fixed to a base
210
by means of a B column
208
. On a carriage
207
for scanning use arranged to move freely with respect to base
210
there is located a mask
202
which is movable a small amount with respect to carriage
207
via a mask stage
203
. A substrate
205
is located such that a substrate stage
206
is movable a small amount with respect to the same carriage
207
(the fixed portions are drawn with thick lines, and the movable portions with thin lines). By scanning the carriage
207
, the mask
202
and substrate
205
scan in a predetermined direction with respect to the projection optical system
204
, and the pattern of the mask
202
successively transfers onto the substrate
205
. A laser interferometer
222
is supported by an A column
209
, and by means of the interference of light reflected from a fixed mirror
211
arranged in the projection optical system
204
and light reflected from a moving mirror
212
arranged in the substrate stage
206
, the position of the substrate stage
206
with respect to the projection optical system
204
is detected. The position information of the substrate stage
206
from the laser interferometer
222
is input into the main control device
240
. The main control device
240
is equipped with a speed adjustment operating unit
218
which outputs speed adjustment instructions according to an exposure program. A servo operating unit
220
calculates and outputs the drive signals for the carriage
207
based on the difference of the speed adjustment instructions and the position information of the substrate stage
206
, and for a drive amplifier
221
which amplifies the output of the servo operating unit
220
. The control unit
217
controls the carriage
207
by means of the output of the drive amplifier
221
. The laser interferometer
222
, main control device
240
and control unit
217
make up a servo loop that controls the carriage
207
. That is, the substrate stage
206
is positioned based on the position information of the substrate stage
206
and the speed adjustment instructions output from the speed adjustment operating unit
218
.
Despite their widespread use, the exposure devices discussed above are not without their problems. For example, in a closed loop control system, the bandwidth or the frequency at which the gain of the closed loop frequency characteristic becomes (½)-fold of the low frequency gain as the frequency &ohgr;→0, and when expressed in dB, falls 3 dB from the low frequency gain of &ohgr;→0.
With a stage control system as shown in
FIG. 6
, the plate stage control performance is set, for example, by means of the response band of the plate stage position and speed control loop during the fixed speed control (uniform speed control) of the plate stage performed in the scanning exposure time, the variable speed, adjustment
Hamada Tomohide
Saiki Kazuaki
Font Frank G.
Lee Andrew H.
Nikon Corporation
Oliff & Berridg,e PLC
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